CUDA kernel doesn't launch

The reason it is not printing when using printf is that kernel launches are asynchronous and your program is exiting before the printf buffer gets flushed. Section B.16 of the CUDA (5.0) C Programming Guide explains this.

The output buffer for printf() is set to a fixed size before kernel launch (see Associated Host-Side API). It is circular and if more output is produced during kernel execution than can fit in the buffer, older output is overwritten. It is flushed only when one of these actions is performed:

• Kernel launch via <<<>>> or cuLaunchKernel() (at the start of the launch, and if the CUDA_LAUNCH_BLOCKING environment variable is set to 1, at the end of the launch as well),
• Synchronization via cudaDeviceSynchronize(), cuCtxSynchronize(), cudaStreamSynchronize(), cuStreamSynchronize(), cudaEventSynchronize(), or cuEventSynchronize(),
• Memory copies via any blocking version of cudaMemcpy*() or cuMemcpy*(),
• Module loading/unloading via cuModuleLoad() or cuModuleUnload(),
• Context destruction via cudaDeviceReset() or cuCtxDestroy().

For this reason, this program prints nothing:

#include <stdio.h>

__global__ void myKernel() 
{ 
  printf("Hello, world from the device!\n"); 
} 

int main() 
{ 
  myKernel<<<1,10>>>(); 
} 

But this program prints "Hello, world from the device!\n" ten times.

#include <stdio.h>

__global__ void myKernel() 
{ 
  printf("Hello, world from the device!\n"); 
} 

int main() 
{ 
  myKernel<<<1,10>>>(); 
  cudaDeviceSynchronize();
} 

Are you sure that your CUDA device supports the SM_20 architecture?

Remove the arch= option from your nvcc command line and rebuild everything. This compiles for the 1.0 CUDA architecture, which will be supported on all CUDA devices. If it still doesn't run, do a build clean and make sure there are no object files left anywhere. Then rebuild and run.

Also, arch= refers to the virtual architecture, which should be something like compute_10. sm_20 is the real architecture and I believe should be used with the code= switch, not arch=.